Glow plug

ABSTRACT

The invention relates to a glow plug comprising a housing, a glow pencil projecting from the housing, and a supply line which is enclosed by the housing and connected to the glow pencil. According to the invention, it is provided that at least one section of the supply line is formed as a flexible metal tube.

The present invention aims at showing a way how the production a glow plug can be simplified.

SUMMARY OF THE INVENTION

In a glow plug according to the invention, at least one section of the supply line is formed as a flexible metal tube. This allows implementing a length compensation element between the glow pencil and an electrical connection of the glow plug in a cost-effective manner. A flexible metal tube is able to adjust flexibly to the length to be bridged and can, therefore, compensate production-related length differences or changes in length the occurrence of which during operation is caused by thermal expansion. For this reason, a flexible metal tube can be used to replace the contact springs that are usually used as length compensation element and to simplify production. Furthermore, a flexible metal tube can be attached to a glow pencil with little effort by inserting one end of the glow pencil into the flexible metal tube and soldering it to the latter. In addition, the flexible metal tube can be easily attached to a connecting element, for example, by inserting the flexible metal tube into a drilled hole of a connecting element and crimping it there, said connecting element being used to connect the glow plug to a voltage source.

Preferably, the flexible metal tube consists of wires, more particularly of metal wires which are interlaced or interwoven with each other. Flexible tubes consisting of interwoven or interlaced metal wires are, sometimes, referred to as metal fabric tubes. It is, for example, also possible to use wrapped tubes in the stead of metal fabric tubes, said wrapped tubes normally being produced by wrapping metal foil up onto a mandrel.

An advantageous further development of the invention provides that, at its end facing away from the glow pencil, the flexible tube is connected to a connecting element. Preferably, the flexible tube is crimped to the connecting element but it can, for example, also be soldered or welded to the connecting element.

Another advantageous further development of the invention provides that the connecting element is enclosed by a plastic body which electrically insulates the connecting element against the housing. The plastic body can be injection-molded around the connecting element in a cost-effective manner.

Preferably, the connecting element is held non-rotatably in the plastic body by a form closure. To achieve this, the connecting element can have projections and/or recesses at an enclosed section, said projections and/or recesses causing a form closure with the plastic body. It is particularly advantageous to interlock the plastic body with the connecting element.

Preferably, the plastic body is held non-rotatably in the housing by a form closure. The plastic body can, advantageously, be pressed into the housing. Since the housing has one or more projections, more particularly projections that extend in longitudinal direction, on its inner side, a form closure can also be generated during pressing-in in addition to a force closure. Most preferably, the plastic body is interlocked with the housing.

Preferably, a glow plug according to the invention has a ceramic glow pencil, but it can also have a glow pencil that is made of metal, more particularly of steel. The advantage of a simple length compensation by means of a flexible metal tube is of particular importance for ceramic glow pencils because the latter are breakable.

In a glow plug according to the invention, the advantage of a simple length compensation can already be utilized if the flexible metal tube forms only a section of the electrical supply line running to the glow pencil. It is, however, preferred that the flexible metal tube forms the supply line between the glow pencil and a connecting element at the rear end of the glow plug,

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantages of the invention will be illustrated by means of an exemplary embodiment with reference being made to the accompanying drawings. In the drawings,

FIG. 1 is a partially sectional view of an exemplary embodiment of a glow plug according to the invention; and

FIG. 2 is an exploded view of the glow plug.

DETAILED DESCRIPTION

The glow plug shown in FIGS. 1 and 2 comprises a housing 1 with a thread 9 and an external polygon 10, preferably an external hexagon. A ceramic glow pencil 2 projects from the forward end of the housing. The glow plug can be connected to a voltage source via a connecting element 3 which, in the illustrated exemplary embodiment, projects from the rear end of the housing 1. Ground connection is achieved via the housing 1.

The glow pencil 2 is electrically connected to the connecting element 3 via a supply line which is enclosed by the housing 1. A special feature of the glow plug shown is that at least one section of this supply line is formed as a flexible metal tube 4. The flexible metal tube 4 consists of wires that are interlaced with each other for which reason it is bendable, with the result that it can act as a length compensation element between the glow pencil 2 and the connecting element 3 for compensating production tolerances or for compensating thermally caused changes in length.

The glow pencil 2 is tapered at its rear end and projects into the flexible metal tube 4 with the tapering section. The flexible metal tube 4 is soldered to the glow pencil 2, for example, by means of a solder wrap 5.

The end of the flexible metal tube 4 that is facing away from the glow pencil 2 can be connected to a section of the supply line, for example, by crimping or soldering. Preferably, the flexible metal tube is inserted into a drilled hole of the connecting element 3 and is crimped there. However, it is also possible to push the flexible metal tube onto an appropriately shaped section of the supply line, for example, a pin-shaped end of the connecting element 3.

The flexible metal tube 4 is enclosed by an electrical insulation 6. The electrical insulation 6 can, for example, be wrapped around the flexible metal tube 4 as a foil. Preferably, the insulation 6 is an insulating tube which encloses the flexible metal tube 4.

The connecting element 3 is enclosed by a plastic body 7 which is pressed into the housing 1. The plastic body 7 was produced by injection-molding around the connecting element 3. The section of the connecting element 3, which is enclosed by the plastic body 7, has elevations and recesses on its outside, said elevations and recesses not being shown. The connecting element 3 is, therefore, held non-rotatably in the plastic body 7 by a form closure. The outer contour of the connecting element 3, which is enclosed by the plastic body 7, can, for example, be formed as a series of tooth grooves extending in longitudinal direction, with the result that the plastic body is interlocked with the connecting element 3.

The plastic body 7 can be held non-rotatably in the housing 1 by a similar form closure. To achieve this, fins or other elevations extending in longitudinal direction are provided on the inner side of the housing 1, said fins or other elevations cutting into the plastic body 7 while the latter is being pressed in and producing a non-rotatable form closure.

The plastic body 7 is flanged into the housing 1. Therein, a flange edge 8 of the housing 1 engages around the plastic body 7.

REFERENCE NUMBERS

-   1 Housing -   2 Glow pencil -   3 Connecting element -   4 Flexible metal tube -   5 Solder wrap -   6 Insulation -   7 Plastic body -   8 Flange edge -   9 Thread -   10 External polygon 

1. A glow plug, comprising: a housing; a glow pencil projecting from the housing; and a supply line for connecting the glow pencil to a voltage source, the supply line being enclosed by the housing and connected to the glow pencil, wherein at least one section of the supply line is formed as a flexible metal tube.
 2. The glow plug according to claim 1, wherein the flexible metal tube is comprised of wires.
 3. The glow plug according to claim 1, wherein the glow pencil projects into the flexible tube.
 4. The glow plug according to claim 1, wherein the flexible tube is soldered to the glow pencil.
 5. The glow plug according to claim 1, wherein the flexible tube, at an end facing away from the glow pencil, is connected to a connecting element.
 6. The glow plug according to claim 5, wherein the connecting element is enclosed by a plastic body.
 7. The glow plug according to claim 6, wherein the plastic body is held non-rotatably in the housing by a form closure.
 8. The glow plug according to claim 6, wherein the connecting element is held non-rotatably in the plastic body by a form closure.
 9. The glow plug according to claim 1, wherein the glow pencil is a ceramic glow pencil.
 10. The glow plug according to claim 1, wherein the flexible metal tube is enclosed by an insulating tube.
 11. The glow plug according to claim 1, wherein the flexible metal tube bridges a gap between the glow pencil and a connecting element.
 12. The glow plug according to claim 1, wherein the housing is electrically connected to the glow pencil for providing a ground connection. 